A pigtailed macaque that was a product of inbreeding (part of a discontinued project) developed an unusual multifocal cutaneous T-cell lymphoma. Diagnostic samples showed this macaque to be negative for a panel of viruses, including Herpes, SIV, CMBV, SRV-1, SRV-5, and STLV-1. However, it is known that a subset of human cases of mycosis fungoides and adult T-cell lymphoma (ATL) cases are HTLV-1 negative. To test the hypothesis that the condition of this macaque is due to a yet-unknown infectious agent, blood was collected at the time of necropsy and transfused to two nave macaques. Blood has been collected from these macaques, and distributed for clinical monitoring (complete blood counts, lymphocyte subset analysis, and serum chemistries) and virological analysis. This work is still underway and results are too preliminary for full analysis. Both macaques are in apparent good health.